The present invention relates to a process and an apparatus for producing ketoisophorone by oxidizing xcex2-isophorone.
Ketoisophorone (4-oxoisophorone) is an useful intermediate product in producing medicines, pesticides, perfumes, condiments, or polymers.
As a method for producing ketoisophorone from xcex2-isophorone, Japanese Patent Application Laid-Open No. 125316 (JP-A-51-125316) discloses a method for producing an ethylenically unsaturated dicarboxylic acid by oxidizing xcex2-ethylenically unsaturated ketone with molecular oxygen or a molecular oxygen-containing gas in the presence of an inorganic base or an organic base and a cobalt or manganese chelate. In this literature, as the solvent, there are enumerated aromatic hydrocarbons, chlorinated aliphatic hydrocarbons, lower aliphatic alcohols, ketones, carboxyamides, nitriles, amines, and ethers.
In Japanese Patent Application Laid-Open No. 53553/1998 (JP-A-10-53553) discloses a method for producing ketoisophorone by oxidizing xcex2-isophorone with molecular oxygen in the presence of a manganese complex salt, an organic base, a specific substance having a catalytic action (e.g., organic acids having a pKa value of 2 to 7) and water. In this literature, the use of a ketone (e.g., acetone, methyl isobutyl ketone) or an ether as a solvent is also described.
According to these methods, however, when the reaction is repeated or the reaction is continuously carried out while circulating the solvent, an oxidizing catalyst is poisoned so that the activity is deteriorated, resulting in failure in maintaining high conversion and selectivity. Moreover, the use of some kind of base may considerably lower the conversion or selectivity of a substrate or causes the isomerization of from xcex2-isophorone to xcex1-isophorone. Particularly, when the concentration of xcex2-isophorone in a reaction system is high (e.g., 20% by weight or higher), the yield of ketoisophorone is considerably reduced.
xcex2-isophorone can be prepared by isomerizing xcex1-isophorone in the presence of an isomerizing catalyst comprised of an acid. For example, in Japanese Patent Publication No. 8650/1979 (JP-B-54-8650) is disclosed a method for producing xcex2-isophorone by the isomerization of xcex1-isophorone in the presence of an isomerizing catalyst (an acid having a pKa value of 2 to 5) followed by distillation. In the literature, adipic acid is exemplified as the isomerizing catalyst and there is described that the continuous isomerization is usually carried out at atmospheric pressure though possible to conduct under reduced pressure.
Accordingly, there may be proposed a process of producing ketoisophorone from xcex1-isophorone by combining the isomerizing reaction and oxidizing reaction. However, when the isomerizing reaction and the oxidizing reaction are employed in combination, the catalyst used in the oxidizing reaction is heavily poisoned, so that the catalytic activity is deteriorated. Therefore, the combination of the isomeriziing reaction and the oxidizing reaction results in difficulty in efficiently and continuously producing xcex2-isophorone.
As a process for producing ketoisophorone from xcex1-isophorone, in Japanese Patent Publication No. 30696/1980 (JP-B-55-30696), Japanese Patent Application Laid-Open No. 191645/1986 (JP-A-61-19164), and Japanese Patent Application Laid-Open No. 93947/1975 (JP-A-50-93947) are disclosed methods for producing 4-oxoisohporone by oxidizing xcex1-ishophorone with oxygen in the presence of a catalyst. Japanese Patent Application Laid-Open No. 81347/1974 (JP-A-49-81347) discloses a method for producing 4-oxoisophorone by oxidizing xcex1-isophorone with an alkaline metal chromic acid salt or a dichromate or a chromium trioxide. In the Chem. Lett. (1983), (7), 1081, there is disclosed a method for producing 4-oxoisophorone by oxidizing xcex1-isophorone with t-butylhydroperoxide in the presence of a palladium catalyst. However, in these methods, since the selectivity to ketoisophorone is low, separation of the formed by-product (s) or a metal catalyst and purification of the object compound are made complicated. Moreover, these methods sometimes involve the use of a heavy metal compound such as chromium which requires special treatment, or a peroxide which is needed to be handled with care, which results in a decrease in working efficiency.
Thus, an object of the present invention is to provide a process and an apparatus for producing ketoisophorone while maintaining the activity of an oxidizing catalyst.
Another object of the present invention is to provide a process and an apparatus for continuously producing ketoisophorone from xcex1-isophorone with high conversion and selectivity while maintaining the activity of an oxidizing catalyst high.
Still another object of the present invention is to provide a process and an apparatus for producing ketoisophorone capable of preventing an oxidizing catalyst from being poisoned even when an isomerization reaction and an oxidizing reaction are employed in combination.
The inventors of the present invention made intensive and extensive studies to achieve the aforementioned objects and found that, in the production process of ketoisophorone in which an inert solvent used in an oxidizing step is reused, a very small amount of impurities (e.g., ketones) present in the solvent poisons an oxidizing catalyst, so that the catalytic activity is considerably lowered. The present invention is based on the above findings.
Thus, the process of the present invention comprises a step for oxidizing xcex2-isophorone in an inert solvent in the presence of an oxidizing catalyst to form ketoisophorone, a step for separating ketoisophorone and the solvent from the reaction mixture, and a step of recycling, at least, the separated solvent to the oxidizing step. In this process, the oxidizing catalyst comprises a complex salt of a transition metal and an N,Nxe2x80x2-disalicylidenediamine. To prevent the deactivation of the oxidizing catalyst, the solvent from which a by-product [particularly, a compont with a low boiling point (impurities of low-boiling point] has been removed in the separation step is recycled to the oxidizing reaction; thereby producing ketoisophorone. The amount of the by-product(s) (impurities of low-boiling point) contained in the solvent to be recycled to the oxidizing step is 0 to 5,000 ppm (weight basis), and examples of the by-product (impurities) include non-conjugated cyclic ketones, and the like. Further, in a preferred embodiment, a solvent substantially free from ketoisophorone is recycled to the oxidizing step.
In the process of the present invention, ketoisophorone may be produced by combining an isomerization reaction and an oxidizing reaction. In this process, the xcex2-isophorone is formed by isomerizing xcex1-isophorone and the xcex2-isophorone thus formed is subjected to the oxidizing step for oxidation.
The present invention also includes an apparatus for producing ketoisophorone which comprises: an oxidizing-reaction unit for forming ketoisophorone by oxidizing xcex2-isophorone with oxygen, in the presence of an oxidizing catalyst, in an inert solvent; a separation unit for separating ketoisophorone, the solvent, and a low-boiling point component having a boiling point of 100 to 180xc2x0 C. as a by-product from the reaction mixture; and a recycling line for recycling the solvent separated in the separation unit to the oxidizing-reaction unit.